1. Field of the Invention
The present invention relates to an FM-CW radar using a transmitted signal which is a frequency-modulated (FM) continuous wave (CW).
2. Related Background Art
The FM-CW radar is suitable for detection of relatively near objects when compared with pulse radars and in recent years research and development is going on to use the FM-CW radar as a means mounted on a car to detect position and relative velocity of an advance car or the like. The FM-CW radars heretofore were, however, arranged to obtain angle information, range information and velocity information of target by mechanical scanning of a fixed beam.
The mechanical scanning has problems of slow scanning rate, incapability of assuring adequate reliability of the mechanical part, and large size of apparatus. These issues become significant particularly in the application for tracking an advance car where the radar is mounted on a car. Specifically, the slow scanning rate tends to delay detection of the target when the azimuth angle of the advance car changes because of lane change, and thus makes it difficult to check the position in real time. Since the scanning mechanism is subject to breakage due to vibration of body etc., it is unavoidable to construct the apparatus in large and heavy structure in order to enhance reliability. There was thus the desire for the FM-CW radar without the mechanical beam scanning mechanism.
On the other hand, there exist digital beamforming (DBF) as a technique to achieve beam scanning by digital signal processing, but no technique for applying this DBF to the FM-CW radar has been established yet.